1. Field of the Invention
This invention relates to a device for producing a multi-layer film composite from plastic films having a number of supply rolls, onto which the plastic films in web form are wound. This invention also relates to a process for producing a multi-layer film composite from films including biaxially stretched thermoplastic, monoaxially stretched thermoplastic and unstretched thermoplastic, coextruded films. The films are laminated to each other with the application of pressure and heat.
2. Background
Various industries, for example apparatus engineering, automotive and aeronautical engineering or safety technology, are taking an increasingly intense interest in high-strength film composites and composite bodies. Such composites typically are in the form of webs as well as of semi-finished products, such as sheet, and as finished components. Following this development, techniques for producing mechanically relatively high-strength products are being developed by sheet manufacturers. Simultaneously with the modification of the polymeric materials provided for sheet production by the incorporation of reinforcing materials such as textile, glass or carbon fibers, techniques are being developed for manufacturing inherently strengthened sheets by orientation mechanisms.
These techniques include roll-press stretching, or the process disclosed in EP-A 0,207,047, which consists of pressing a plurality of biaxially stretched films treated with thin coextruded sealing layers under the application of pressure and heat to form a homogeneous sheet of any desired thickness. To this end, the stack of films inserted between two press plates typically is introduced into a batch-operation such as hydraulic platen presses of single or multi-platen design. The pressing operation is governed by process parameters such as pressure, temperature and time. Time, in particular stands in the way of economical production of composite laminates, especially in the case of through-heating very thick sheets. Continuously operating presses, especially double-belt presses, represent a practical, time-saving solution in this regard, but can only be used to a limited extent due to their speed of operation.
German Patent 35 30 309 discloses a process and a device for the continuous production of thermoplastic webs, especially for further processing to sheets or films, from at least one extruded thermoplastic web. The web typically is heated to processing temperature, and is cooled under pressure while in the heated state between two stationary plates so that the surface of the thermoplastic web is sized and smoothed. The cooling of the thermoplastic web takes place under the effect of surface pressure, and the web is guided, during cooling, between two continuously moving, endlessly circulating press belts.
A uniform surface pressure is exerted from the plates hydraulically or mechanically onto the inner side of the moving press belts and transmitted from these to the thermoplastic web. The plates typically are held at a lower temperature than the final temperature of the thermoplastic web in order to maintain a temperature gradient between the thermoplastic web, the press belt and the plate. Cooling of the thermoplastic web generally takes place by heat dissipation from the web via the press belt to the plates by thermal conduction. During normal operation, the surface pressure acts throughout the cooling of the thermoplastic web between the press belts.